Traditionally, telecommunication services have been provided by the Public Switched Telecommunication Network (PSTN). In this type of network, a service (typically a telephone call) is preceded by signaling to request and accept a connection. Signaling at the beginning, during, and at the end of a service is used for charging the service. Charging can be implemented in non-real-time or postpaid mode via charging records produced by the signaling entities, or in real-time mode (mandatory in prepaid billing) where an account is identified, reserved and charged in the course of signaling interactions.
This charge model is applicable to call or session billing, both for connection and usage (e.g. duration, traffic) charges. The model is also applicable to content billing, when each request for separately charged content comprises signaling for requesting and accepting the delivery of the content. Although the latter negotiation for content billing happens on a higher protocol level than call or session setup signaling, signaling is distinct from the chargeable content delivered to the user.
In the telecommunications world, simple services delivered in high volume may have a fixed price negotiated in advance by network operators, e.g. the price per minute for a call from a subscriber A1 of network operator A in the United States to a subscriber B1 of network operator B in Australia. On a subscriber level, subscriber A1 knows the price charged per minute by operator A for a call to subscriber B1, and on an operator level, operator A knows the price charged by operator B or a transit operator to deliver the call from operator A's network to subscriber B1. This is known as origin charging, or “bill and keep”. When this is the only model used for service charging, charges can be predetermined by access operator A.
More complex services cannot be handled as described above, i.e. when the service delivered cannot be counted in connections, duration or traffic. Examples would be expert hotlines provided over premium rate numbers, or downloads of variably priced music titles from an online store. In such cases, the service provider would need to determine the appropriate charge during the actual service delivery, and an example of this type of charge is called termination or service provider charging. Typically, termination charging is simple when the service provider has a direct billing and collection contract with the network operator of an end user or subscriber who uses the service.
On the other hand, in today's multi-carrier world, conventional termination or service provider charging would require significant effort by the service provider's network operator to filter calls to the service from many other networks. An inordinate effort may be required of the service provider to connect to all potential networks to which service may be desired. Either the service provider or the network operator has to find out which network operator a service request originates from, and determine whether a service request should be accepted or refused. When the request originates from an operator that has a bilateral invoicing and collection agreement with the service provider's operator (“good case”) the service may be delivered. When the service request originates from another operator without a billing relationship (“bad case”), service is refused. It is straightforward to determine the requestor's operator in the operators own network, but it may be very difficult to identify the originating network identification for calls coming from other networks, since the interconnection partner may be the access network operator for the subscriber requesting the service or may be just a transit network operator. Determining the originating operator by caller number inspection may be problematic in networks where Number Portability is possible. A database query has to be performed to determine the originating network operator from the network supplied Calling Line Identifier. In many countries, reliability of Number Portability database information is limited, particularly close to the porting time. This opens up specific possibilities for error or fraud relating to identification of the originating operator for termination billed services. The same issues may arise for email addresses, signatures and other subscriber identifications. With respect to potential email address portability, because an email address, is a globally unique user identifier, just like a E.164 telephone number, it is not clear yet whether an address like first.last@aol.com would have to be ported to another access network operator, or whether users who want portability would be required to register their own domain with email addresses, e.g. me@first-last.net. In any case, it would not be trivial to find out the current originating access network operator for a user with a specific email address, or SIP URI.
So, for termination billing, in addition to transporting the user identity, there is a need to transport the originating network identity reliably to determine service availability. In a conventional PSTN network, transport of the originating network identification has been proposed in Germany for the signaling network, using an Originating Network Identification Parameter (ONIP). By providing the originating network identification using ONIP in a PSTN network, bilateral invoicing and billing has been practised successfully in PSTN networks because it is relatively difficult for hackers to access and manipulate such information in a dedicated PSTN network. Nevertheless, IP based networks are potentially more open to such threats and fraudulent activity, and thus improved integrity protection of the originating operator identity is needed to enable a terminating network to identify and verify (i.e. authenticate) an originating network identification more reliably for billing purposes in IP networks.